To secure your machine, there are hundred different things you can do, but the most important thing is to know what's happening on your Machine. In that getting the alerts as soon as someone login is one of very important and must thing to do.

When it come to optimization of a site or web-server, ETAGs and Expiry headers are the two main things you should be looking at. ETAGs and Expiry headers will be used to understand by the client whether to fetch the latest file or not, but still there is a difference between these two and are used at different scenarios.

The Basic working of the screen is already explained in my previous article and if you are not really looking for advanced screen features, you should look at my previous screen article. The link for the same is: Basics of GNU Screen

But there are a lot of advanced features which screen provides which might come handy in a lot of scenarios. I will be explaining them under.